The agreement should secure enough bipartisan support for the Senate to proceed to debate on an overarching bill that would expand background checks, make gun trafficking a federal crime for the first time and bolster federal funding for school security plans. Senate Democratic leaders have said they will permit senators of both parties to introduce amendments to the measure.

Sens. Joe Manchin, D-W. Va., Chuck Schumer, D-N.Y., Pat Toomey, R-Pa., and Mark Kirk, R-Ill., have been working on the deal, and will introduce it as a possible amendment to the Senate's broader gun control package.

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Majority Leader Harry Reid said Tuesday that the Senate will hold a preliminary vote on Thursday to try to break a Republican filibuster and proceed with a debate on the bill. Democrats appear to have secured enough votes to break the filibuster after a number of Republicans broke ranks and said they would support initiating debate, though it's unclear what the bill's fate will be beyond that.

Jillian Rayfield

Jillian Rayfield is an Assistant News Editor for Salon, focusing on politics. Follow her on Twitter at @jillrayfield or email her at jrayfield@salon.com.